A voltage follower is a semiconductor device which outputs a potential that is equivalent to an input potential. In a semiconductor integrated circuit which is an example of a semiconductor device, the voltage follower can be used as a buffer of a potential generating circuit.
In addition, with the use of two voltage followers, an input potential signal can be held (Patent Document 1).
Meanwhile, in recent years, metal oxides having semiconductor characteristics (hereinafter referred to as oxide semiconductors) have attracted attention. Oxide semiconductors may be applied to transistors (see Patent Documents 2 and 3).